A student heated 12.0 g of calcium carbonate in an open crucible and obtained 6.7 g of solid. Which evaluation is correct?
Answer and explanation
Correct answer: Carbon dioxide was produced by the decomposition of calcium carbonate and escaped from the open crucible; total mass would be conserved in a closed system.
During thermal decomposition, \(\mathrm{CaCO_3(s) \rightarrow CaO(s) + CO_2(g)}\). Since 100 g of \(\mathrm{CaCO_3}\) produces 56 g of \(\mathrm{CaO}\), 12.0 g should produce \(12.0 \times 56/100 = 6.72\) g of solid, consistent with 6.7 g. The \(\mathrm{CO_2}\) gas escapes from the open crucible, so weighing only the solid gives a lower mass. In a closed system, the combined mass of the solid and gas remains conserved.
Frequently asked questions
What is the correct answer to this question?
Carbon dioxide was produced by the decomposition of calcium carbonate and escaped from the open crucible; total mass would be conserved in a closed system.
Why is this the correct answer?
During thermal decomposition, \(\mathrm{CaCO_3(s) \rightarrow CaO(s) + CO_2(g)}\). Since 100 g of \(\mathrm{CaCO_3}\) produces 56 g of \(\mathrm{CaO}\), 12.0 g should produce \(12.0 \times 56/100 = 6.72\) g of solid, consistent with 6.7 g. The \(\mathrm{CO_2}\) gas escapes from the open crucible, so weighing only the solid gives a lower mass. In a closed system, the combined mass of the solid and gas remains conserved.
Which subject and chapter does this question cover?
This is a Class 10 Science question. Chapter: Chemical Substances – Nature and Behaviour. Topic: Chemical Reactions and Equations.
